Powder sampler

ABSTRACT

A sampling device for obtaining representative samples of material from a bulk quantity thereof includes a plurality of rotating sample containers which are sequentially and repetitively fed by a flow stream of the material. The flow stream eminates from a hopper. The mechanism controls the flow rate of the flow stream to insure representativeness and statistical validity of the samples.

United States Patent Jackson [4 1 June 6, 1972 [54] POWDER S AIVIPLERPrimary Examiner-Houston S. Bell, Jr.

Attomey-E. Manning Giles, J. Patrick Cagney, Michael A. [72] Inventor:Meryl R. Jackson, Schaumburg, Ill. Kondzena and Richard zachar [73]Assignee: Freeman Laboratories, 1nc., Rosemont, Ill.

[57] ABSTRACT [22] Filed: Oct. 21, 1970 A sampling device for obtainingrepresentative samples of PP 32,686 material from a bulk quantitythereof includes a plurality of rotating sample containers which aresequentially and repeti- [52] us'clm "141/130, 141/102. 1431 tively fedby a flow stream of the material. The flow stream 51 Int. Cl ..B65b 4350 eminaies from P mechanism 58 Field of Search ..l4l/l30-l34, 256.Stream m insure Presemafiveness and 141/183-191, 267, 268. 102; 73 424statistical validity of the samples.

56 References Cited 7 Chums 2 Drawing FORElGN PATENTS OR APPLICATIONS11/1951 Germany ..l41/132 PATENTEDJUH 6 :972

FIG. I

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I INVENTOR MERYL R. JACKSON BY W 2AM ATTORNEY POWDER SAMPLER BACKGROUNDOF THE INVENTION The present invention relates to sampling devices forobtaining representative samples of material from a bulk quantity ofmaterial.

Particulate materials used in a process often at some time or anothermust be withdrawn from a larger mass of material. The sample withdrawnmay be used in the actual process or may be used for analysis as acontrol. Wherever it is assumed that the sample is the same, orrepresentative of the bulk material, that sample must be obtained in astatistically valid manner.

It is difficult to obtain a representative sample of material from abulk quantity of a mixture of particles in a fluid. If the mixture isfreely flowing like dry sand in air, the large particles tend toseparate from the small ones and locate at one or more boundaries withinthe mixture. In the case of cohesive materials, like cornstarch orviscous pastes, it is difficult to cause the material to flow so thatsampling from the entire mixture is impossible.

Many techniques have been proposed and are being used for samplingpowders and suspensions. In the simplest technique a sample of powder orsuspension is removed from the exposed surface of the bulk material,using a scoop or similar receiver. This method gives samples which havebeen taken from the outer areas of the material and are thus liable tobe non-representative of the bulk. The technique is used extensivelysince it is rapid and inexpensive, but it is unsuitable for freelyflowing powder since'these roll off the scoop.

Another method involves the insertion of a sample tube or thief into thebody of the mixture to be sampled. A concentric door may be opened andclosed to obtain a sample from a particular location and then allow thethief to be withdrawn with the sample inside. This technique is usedextensively in boxcar and other bulk sampling but has an extremely lowefficiency. Samples are representative of only the location sampled anddo not necessarily relate to the composition of the bulk. Highlycohesive powders tend to remain outside the thief when the door isopened and do not flow into the sample cavity.

In another technique, called cone and quartering, the bulk material isallowed to form into a heap or cone. A large knife-like blade isinserted vertically into the cone to divide it into two mirror-imagefractions. One fraction is removed and the blade then insertedvertically into the remaining fraction to divide it into twomirror-image fractions. One of these is then discarded to leave aquarter of a cone having approximately one quarter the volume of theoriginal bulk sample. This technique reduces errors arising as aconsequence of segregation of material, but theoretically relies onthere being a cone having perfect symmetry about its vertical axis. Inpractice, this is not achieved and therefore the method is subject toerror. In addition, the technique is relatively slow, requires manualeffort, invites sample contamination and tends to introduce dusting withconsequent loss of fine material.

Yetanother technique involves the use of a table having an inclinedslotted surface. Material sliding down the incline is split into twofractions by guides. One half is discarded down a slot while the otherhalf slides to a second set of guides and is subdivided into two partsagain. Three stages of division are usually provided on a table. Thistechnique is poor and gives samples having a wide range of composition.Efficiency is determined by the method of filling and is hence operatordependant.

Still another technique involves the use of apparatus consisting of aV-shaped trough containing ten or more shoots feeding, alternately, twotrays placed on either side of the trough. Efficiency of sampling isdependant, when using this technique upon the number of shoots, theirsize relative to the size of the largest particle in the mixture, themethod of filling the trough and the exact geometry of the system. Themethod is capable of dividing the sample by two, only, and is generallyinefficient in giving representative samples of small volumes ofmixtures. In a somewhat similar approach, material is held in a hopperand allowed to freely flow through the throat of the hopper and into aplurality of rotating trays. Highly cohesive powders and viscous pastestend to choke the shoots (or throat of the hooper) and do not flowfreely and freely flowing materials tend to be subject to boundaryformation.

A need therefore exists for a means of obtaining a representative sampleof material from a larger batch or bulk of the material which means canbe used both in the case of extremely freely flowing materials or highlycohesive materials, the sample being statistically valid and identicalin composition to the original batch.

SUMMARY OF TI-IE INVENTION In satisfying this need, the sampling deviceof the present invention makes use of a receiver that is subdivided intoa plurality of radially oriented sample containers. A hopper-likecontainer or funnel is supported above the receiver and holds the bulkmaterial tobe sampled. The container has a bottom outlet opening orthroat in communication with a metering system which operates to causematerial flow at a substantially time-uniform rate from the containerinto the sample compartments of the receiver, which is caused to berotated.

In the preferred embodiment illustrated herein, the metering meanscomprises an auger screw coaxially mounted within an auger tube. Byvarying the clearance between the auger tube and the auger screw, alltypes of wet and dry mixtures can be representatively sampled on astatistically valid basis.

Other features and advantagesof the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawings which show structure embodying preferred features of thepresent invention and the principles thereof, and what is now consideredto be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE PREFERREDEMBODIMENT With reference now to the drawings, a sampling device l0 inaccordance with the present invention is shown to comprise a mixturereceiver 12 that is subdivided into a plurality of sample containers l4and which is rotatably supported on a rotating table 16 that is driventhrough a shaft 18 by a motor 20. The bulk material or mixture to besampled is contained within a supply hopper or funnel 22 which issupported by suitable support structure 24 in elevated relation to thereceiver 12. A flow-rate control mechanism 26 is fed with the bulkmaterial and operates to transport at a substantially timeuniform ratethe material from the throat 32 of the supply hopper 22 horizontally toa discharge position 34 above the receiver 12. As illustrated in FIG. 2,the sample containers are pie-segment in shape and are disposed, whenthe receiver is placed on the rotary table 16, such that the materialexiting from the flow rate control mechanism 26 falls sequentially intoeach sample container as it passes under the outlet 34. The speed ofrotation of the receiver 12 is selected to minimize loss of fine powdersby windage, but rapid enough, as will be explained more fully below, sothat each sample container 14 is presented to the material flow stream asufficient number of times, preferably at least 30 times, to insurestatistical validity.

As suggested above, the function of the flow rate control mechanism 26is to insure that the containers 14 receive representative samples ofthe material flow and to insure, through control of the flow rate, thatthe containers sample the flow stream a sufficient number of times toprovide statistically valid samples regardless of the flowcharacteristics of the bulk material or mixture to be sampled. Since thequality of the stream material is variable with time, in order to obtaina representative sample in each of the containers 14, the samplecollected in each cup must comprise a number of small samples collectedat a number of points in time. In this way the variability of the streamis averaged out. In this connection it will be noted that since thespeed of rotation of receiver 12 is finite, the stream flow rate mustalso be finite if each container 14 is to be presented to the stream anumber of times. Thus, the material in the hopper 22 should not beemptied in a time period comparable to or less than the time forrotation of table 16. If this were to occur the sample containers 14would contain a mixture whose quality would be determined by thecharacteristic of the stream as a function of time. Thus, the flow ratecontrol device 26 is provided to ensure that the material is dischargedfrom the hopper over a time period corresponding to at least 30rotations of the table 16.

In the presently preferred embodiment, the flow rate control mechanismcomprises an auger assembly that includes a horizontal tube 30 having amaterial receiving opening 32' communicating with the bulk quantitythrough the hopper throat 32 and a material discharge opening 34"communicating with the sample containers 14. A screw 28 which extendsbetween the spaced openings 32 and 34' and is rotatively driven by asuitable motor 36 completes the auger and operates to transport materialupon its rotation from opening 32' to opening 34'. When the bulkmaterial is wet or has high cohesive properties, the auger screw 28should have an outer diameter substantially equal to the inner diameterof the auger tube so as to eliminate the tendency of cohesive materialsand pastes to cake onto the inner surface of the auger tube. In the caseof bulk materials consisting of relatively large particles, a clearanceshould be maintained between the auger screw and the auger tube toprevent crushing the particles. Proper clearance between the auger screwand tube can be accomplished either by changing the auger screw itselfor by inserting a suitable sleeve (not shown) into the auger tube toreduce the effective inner diameter thereof.

The pitch, diameter and speed of rotation of the screw are selected toprovide a predetermined rate of delivery and, hence, the assembly 26 maybe considered to be a metering device. ln the embodiment illustratedherein for use in laboratory testing, a rotation rate of 25 rpm for a 1inch diameter screw having a pitch between one-half to 1 inch hasproduced excellent results for both wet and dry materials.

The storage hopper 22 is provided with an electromagnet or other type ofvibrator 40 which moves the walls or one wall of the hopper near itsthroat. This action breaks arches formed in cohesive powders and helpsmaintain a flow of powder from the hopper to the feeder 26. To furtherregulate the flow rate of freely flowing mixtures and to therebymaintain the statistical validity of sampling by insuring that thecontainers are presented a sufficient number of times to the flowingstream of mixture, the throat 32 of the supply hopper 22 can be variedin size. Thus, for example, a removable false wall 38 is illustrated inphantom in FIG. 1 for this purpose.

While preferred constructional features of the invention are embodied inthe structure illustrated herein, it is to be understood that changesand variations may be made by those skilled in the art without departingfrom the spirit and scope of the appended claims.

What is claimed is:

l. A sampling device for obtaining representative samples of materialfrom a bulk quantity thereof and including first means for funneling thebulk quantity to produce a material flow stream, a plurality of samplecontainers, second means for sequentially and repetitively moving saidsample containers individually into intercepting relation with said flowstream whereby said sample containers each intermittently receivesmaterial which is only a portion of a sample from the bulk quantity sothat a sam le is built up in each of said sample containers over aperiod 0 time after repetitive movement Of said sample containers intosaid intercepting relation with said flow stream, said device beingcharacterized in that said first means includes mechanism for effectinga substantially timeuniforrn and continuous flow rate of said flowstream.

2. A sampling device in accordancewith claim 1 wherein the effected flowrate relative to the repetition rate of said sample containers is suchthat each of said sample containers moves through intercepting relationwith said flow stream at least approximately 30 times prior toexhaustion of the bulk quantity.

3. A sampling device in accordance with claim 1 wherein said mechanismincludes an elongated tube having spaced material receiving anddischarge openings, a screw rotatively mounted coaxially within saidtube, and means for axially rotating said screw for producing axial flowof material from the receiving opening to the discharge opening.

4. A sampling device in accordance with claim 3 wherein the diameter ofsaid tube, the pitch of said screw and the speed of rotation of saidscrew are such as to produce an axial flow rate relative to therepetition rate of said sample containers such that each of said samplecontainers moves through intercepting relation with said flow stream atleast approximately 30 times prior to exhaustion of the bulk quantity.

5. A sampling device for obtaining representative samples of materialfrom a bulk quantity thereof and including first means for funneling thebulk quantity to produce a material flow stream, a plurality of samplecontainers, second means for sequentially and repetitively moving saidsample containers individually into intercepting relation with said flowstream whereby said sample containers each intermittently receivesmaterial which is only a portion of a sample from the bulk quantity sothat a sample is built up in each of said sample containers over aperiod of time after repetitive movement of said sample containers intosaid intercepting relation with said flow stream, said device beingcharacterized in that said first means includes mechanism for effectinga substantially timeuniform and continuous flow rate of said flow streamregardless of the natural flow characteristic of the material of thebulk quantity to be sampled, said mechanism including a tube having amaterial receiving opening in communication with the funneled bulkquantity and a material discharge opening in communication with saidsample containers, and a screw rotatively mounted within said tube andextending between the openings for axially transporting upon rotationthereof material from said material receiving opening to said materialdischarge opening.

6. A sampling device in accordance with claim 5 wherein the diameter ofsaid screw and the inner diameter of said tube each is approximately 1inch, said screw having a pitch between about one-half to 1 inch and arotation rate of about 25 rpm.

7. A sampling device in accordance with claim 5 and further includingmeans for varying the effective size of said material receiving openingin accordance with the flow characteristic of the material.

1. A sampling device for obtaining representative samples of materialfrom a bulk quantity thereof and including first means for funneling thebulk quantity to produce a material flow stream, a plurality of samplecontainers, second means for sequentially and repetitively moving saidsample containers individually into intercepting relation with said flowstream whereby said sample containers each intermittently receivesmaterial which is only a portion of a sample from the bulk quantity sothat a sample is built up in each of said sample containers over aperiod of time after repetitive movement of said sample containers intosaid intercepting relation with said flow stream, said device beingcharacterized in that said first means includes mechanism for effectinga substantially timeuniform and continuous flow rate of said flowstream.
 2. A sampling device in accordance with claim 1 wherein theeffected flow rate relative to the repetition rate of said samplecontainers is such that each of said sample containers moves throughintercepting relation with said flow stream at least approximately 30times prior to exhaustion of the bulk quantity.
 3. A sampling device inaccordance with claim 1 wherein said mechanism includes an elongatedtube having spaced material receiving and discharge openings, a screwrotatively mounted coaxially within said tube, and means for axiallyrotating said screw for producing axial flow of material from thereceiving opening to the discharge opening.
 4. A sampling device inaccordance with claim 3 wherein the diameter of said tube, the pitch ofsaid screw and the speed of rotation of said screw are such as toproduce an axial flow rate relative to the repetition rate of saidsample containers such that each of said sample containers moves throughintercepting relation with said flow stream at least approximately 30times prior to exhaustion of the bulk quantity.
 5. A sampling device forobtaining representative samples of material from a bulk quantitythereof and including first means for funneling the bulk quantity toproduce a material flow stream, a plurality of sample containers, secondmeans for sequentially and repetitively moving said sample containersindividually into intercepting relation with said flow stream wherebysaid sample containers each intermittently receives material which isonly a portion of a sample from the bulk quantity so that a sample isbuilt up in each of said sample containers over a period of time afterrepetitive movement of said sample containers into said interceptingrelation with said flow stream, said device being characterized in thatsaid first means includes mechanism for effecting a substantiallytime-uniform and continuous flow rate of said flow stream regardless ofthe natural flow characteristic of the material of the bulk quantity tobe sampled, said mechanism including a tube having a material receivingopening in communication with the funneled bulk quantity and a materialdischarge opening in communication with said sample containers, and ascrew rotatively mounted within said tube and extending between theopenings for axially transporting upon rotation thereof material fromsaid material receiving opening to said material discharge opening.
 6. Asampling deviCe in accordance with claim 5 wherein the diameter of saidscrew and the inner diameter of said tube each is approximately 1 inch,said screw having a pitch between about one-half to 1 inch and arotation rate of about 25 rpm.
 7. A sampling device in accordance withclaim 5 and further including means for varying the effective size ofsaid material receiving opening in accordance with the flowcharacteristic of the material.